Anyone who has been asked to leave their address can gather at the Community Centre on Rolleston Drive.
The blaze started on a Knights Rd property and has since spread across paddocks.
Ground conditions in the area are dry.
Rolleston Fire (longer)
Posted by AshburtonTV on Friday, 22 December 2017
Local man Jason Shaw said the fire was at least two storeys high.
"There's this huge hedge on fire ... on a farm on the outskirts of Rolleston," he said.
He'd spoken to a relative at Christchurch Airport, about 20km away, who said they could see the smoke from there.
"It's massive alright."
Ashburton TV director Tony Arthur happened to be driving past when he came upon the huge blaze.
"It looked like trouble alright, it really did," Arthur said.
"With the high winds it looked like it could have crossed the road easily. It probably had by the time we left to be honest."
Helicopters with monsoon buckets were attacking the fire until night fell.
A second large fire near Coutts Island also broke out this afternoon.
The Fire and Emergency spokesman said eight tankers and three fire engines were fighting the blaze. Firefighters were working with heavy machinery and pumps to wet down t site.
Crews were set to stay at the scene overnight.